Method and apparatus for reducing inrush current in a multi-stage compressor

A compressor assembly for compressing a vapor, said compressor assembly comprising:

• a suction inlet;
• a first housing;
• a first compression mechanism and a first motor operably coupled to said first compression mechanism, said first compression mechanism compressing the vapor from a low pressure to an intermediate pressure, said first compression mechanism and said first motor mounted in said first housing, said first compression mechanism in fluid communication with said suction inlet;
• a discharge outlet;
• a second housing;
• a second compression mechanism and a second motor operably coupled to said second compression mechanism, said second compression mechanism compressing the vapor from the intermediate pressure to a discharge pressure, said second compression mechanism and said second motor mounted in said second housing, said second compression mechanism in fluid communication with said discharge outlet, said second compression mechanism downstream of said first compression mechanism and in fluid communication therewith;
• and
• an electrical circuit supplying electrical current to said first and second motors during operation of said compressor assembly, said electrical circuit including means for, during start-up of said compressor assembly, initiating the supply of electrical current to said first motor at a first time and initiating the supply of electrical current to said second motor at a second time wherein said first time precedes said second time by a time lapse.

A compressor assembly for compressing a vapor, said compressor assembly comprising:

• a housing including a suction inlet and a discharge outlet;
• a first compression mechanism and a first motor operably coupled to said first compression mechanism, said first compression mechanism compressing the vapor from a low pressure to an intermediate pressure, said first compression mechanism and said first motor mounted in said housing, said first compression mechanism in fluid communication with said suction inlet;
• a second compression mechanism and a second motor operably coupled to said second compression mechanism, said second compression mechanism compressing the vapor from the intermediate pressure to a discharge pressure, said second compression mechanism and said second motor mounted in said housing, said second compression mechanism in fluid communication with said discharge outlet, said second compression mechanism downstream of said first compression mechanism and in fluid communication therewith;
• and
• an electrical circuit supplying electrical current to said first and second motors during operation of said compressor assembly, said electrical circuit including means for, during start-up of said compressor assembly, initiating the supply of electrical current to said first motor at a first time and initiating the supply of electrical current to said second motor at a second time wherein said first time precedes said second time by a time lapse.

A method of initiating operation of a multi-stage compressor assembly having a suction inlet and a discharge outlet, said method comprising:

• providing a first motor for driving a first compression mechanism, said first compression mechanism compressing a vapor from a first, low pressure to a second, intermediate pressure during operation of said first compression mechanism said, first compression mechanism in fluid communication with the suction inlet;
• providing a second motor for driving a second compression mechanism, said second compression mechanism compressing the vapor from the second, intermediate pressure to a third, discharge pressure during operation of said second compression mechanism, said second compression mechanism in fluid communication with the discharge outlet, said second compression mechanism downstream of said first compression mechanism and in fluid communication therewith;
• supplying electrical current to said first motor to initiate operation of said first motor at a first time;
• and
• supplying electrical current to said second motor to initiate operation of said second motor at a second time wherein said first time precedes said second time by a time lapse.